40mm Bofors L/60
The 40mm Bofors L/60 is an autocannon produced primarily during the Second World War and used in at least some capacity by all major powers on both sides, primarily serving as an anti-aircraft gun. It was used in both ground and ship-mounted roles. While it has largely been replaced in first-world armies, it is a common sight in conflict zones, and has even retained niche roles in first-world armies such as being used on American AC-130 gunships. The gun is typically referred to as the L60 or L/60 in modern sources to differentiate it from the later 40mm Bofors L/70 chambered for the larger 40×364mmR round, despite that only the WW2 Japanese version actually had a barrel of this length. All other wartime variants used a barrel 56.25 calibers long. History The lineage of the Bofors can be traced back to a 1918 design by Krupp, though the final weapon owes almost nothing to its ancestor. Much like the original Swiss version of the Oerlikon L70, the M1936 gun as designed by Bofors was in no way suited for mass production. Swedish production diagrams dictated a process involving excessive amounts of hand-finishing, with many instructions to "file to fit at assembly" or "drill to fit at assembly." One American production engineer is said to have joked that the gun was clearly designed "so as to eliminate the unemployment problems of the Great Depression." The US Navy also rejected the provided twin-mount design as it was not power-assisted or water-cooled, and rejected the Swedish HE ammunition as unsafe and unsuited for mass production. The British made sweeping changes to the design in this regard, with the Chrysler Corporation using the British design as a basis and making even more alterations. Chrysler made major changes to ten components, and it was claimed these saved 7,500,000 pounds (3,402,000 kg) of material and 1,896,750 man-hours over the course of a year of production. 40mm L/60s were not available to the US Navy in quantity until 1943, but as production picked up they quickly became the preferred anti-aircraft armament, being retrofitted to virtually every class of US warship with the Iowa-class battleships each equipped with eighty. Often they used an aiming director, a pedestal mounted version of the lead-calculating electromechanical Mk 14 Gyro Gunsight for the 20mm Oerlikon called the Gun Director, Mk 51. Up to four power-assisted Bofors gun mounts (hence up to sixteen guns) could be slaved to the point-of-aim of a single gun director, allowing for extremely focused anti-aircraft fire. This proved to be one of the few effective methods of stopping high-speed Japanese kamikaze attacks in the final years of the Pacific campaign. Postwar, the US Army still regarded the L/60 as a viable weapon system. In 1945 twin 40mm Bofors L/60s were used to arm the M24 Chaffee-based M19 Multiple Gun Motor Carriage, and in 1952 the same armament was used on the M41 Walker Bulldog-based M42 Duster self-propelled AA gun (SPAAG). The latter were used in Vietnam, often in an unintended anti-infantry role: while they started to be replaced in their AA role by the M61 Vulcan-based M163 VADS in 1969, they continued to be used by the US National Guard until 1988. However, with the development of fast jets and reliable long-range, precision-guided weapons, the 40mm Bofors finally began to show its age, with most countries still operating it as an AA gun adopting MANPADS in the 70s and 80s to replace it. In the very low altitude air defense role for engaging aircraft forced down low by SAM coverage, it was replaced by faster-firing guns such as the 35mm Oerlikon GDF. The most recent use of the L/60 was arming the AC-130, a development of the C-130 Hercules transport plane armed with a variety of direct-fire weapons for conducting close air support. The early AC-130A mounted two, while the E model replaced one of these with a 105 mm howitzer. These weapons were mostly taken from mothballed M42 Dusters: according to some stories, when four more AC-130s were converted in 2002, the guns had to be sourced from vehicles found on a firing range. While the latest AC-130J and W variants do not mount Bofors guns, other existing variants still carry them. Design Details The 40mm Bofors is a long recoil-operated weapon using a vertically sliding block, with automatic loading using a gravity feeder and ramming tray. The gun is select-fire with both semi and auto settings, with the fire selector a pointer-like lever on one side of the breech assembly near the rear. It can also be operated manually, though this was only for emergency use if there was something wrong with the automatic feed system. Most variants of the gun eject directly rearwards, but employ a series of deflectors and chutes to redirect spent casings to eject from the front of the gun mount. The sliding block operates in a manner resembling a falling block action: in this case, though, the movement of the block is controlled by a cam surface that mates with a roller on a crank set attached to the block. This crank is also attached to the shaft of the closing spring. As the gun recoils, the angled cam surface forces the cranks to lower the block, allowing for extraction of the spent casing and tensioning the closing spring: as it returns to the forward position, there is time for the ramming tray to chamber a new round before the cams are released and the breech closed by the tensioned spring. A large operating handle resembling a steam train's brake lever mounted on the side of the gun is pulled back to lower the block in order to chamber the first round. The fundamental operation of aiming and firing most mountings was handled by two men. The crewman on the right side of the mount, the "trainer," was responsible only for traversing the gun, while the man on the left, the "pointer," was responsible for elevation, and also firing the gun using a foot-pedal. Both operators had their own gunsight, and coordinated their efforts to aim the weapon. In manually operated mountings, each operator had a two-handed crank in front of them to perform their part of the aiming operation. While feeding and ejection are ambidextrous, the fire controls are only on one side. As a result, "left" and "right" guns had to be manufactured for multiple gun mounts with their controls on the relevant side. The reversed components were the hand operating (cocking) lever, fire selector, trigger mechanism and firing plunger, access doors for the breech mechanism, and extractor release levers. US quad mounts would have the guns spaced in two pairs, each of a left and a right gun. Ammunition The Bofors L/60 fired the [[40×311mmR|'40×311mmR']] round, a heavy 1.57 inch projectile. Most ammunition intended for anti-aircraft use had some kind of high-explosive element and was fitted with a timed self-destruct fuze to prevent friendly fire damage from misses. Non-explosive armor-piercing ammunition was also issued. The gun used a gravity feeder which was part of the automatic loader assembly as its ammunition source: this was loaded using four-round clips. It was typically loaded with complete clips and so the capacity is normally given as eight rounds, though in practise it could contain up to ten if two loose rounds were loaded between clips. On loading, the clip was immediately stripped from the first set of four rounds and dropped out of the bottom of the gun through a chute. The second set pushed in would be used to force a round through the feed rollers (a pair of four-pointed star wheels) and into the gun's ramming tray: this only needed to be performed once on initial loading. After two rounds were fired, the second clip would drop out of the gun. While they look somewhat similar from a distance, the feed guides are more complex than the clip guides commonly found on rifles, incorporating a series of feed and stop pawls operated as the weapon's action cycles to regulate the motion of loaded rounds. To protect the feed system from accidental damage in transit and prevent water or debris from entering the gun's action when it was not in use, a cover was provided for the feeding system: this was simply a hollow metal box with sloped sides and a pair of side handles for lifting, and could be placed or removed by a single man. Typically there would be two loading crewmen per gun: the first would retrieve clips from wherever they were stored and bring them to the second. The second stood up on the platform of the gun and actually loaded them into the weapon. To speed up loading, the first loader would pass the clips up already oriented with respect to the barrel axis, so all the second loader had to do was push them in. Standard provision of ammunition per gun was 1,562 rounds on Royal Navy vessels and 2,000 rounds on US Navy vessels. Variants If the Autocannon has any major variants, they may be entered in this section. (Remove if not required) References * TM 9-252 "40-mm Automatic Gun M1 (AA) and 40-mm Antiaircraft Gun Carriages M2 and M2A1," War Department, 17th January 1944. * Ordnance Pamphlet No. 820 "40 mm Antiaircraft Gun," Department of the Navy Bureau of Ordnance, October 1943. Category:Autocannons Category:Anti-aircraft weapons Category:Mounted guns